God characters in anime are such an oxymoron half the time... Most of them can die, and usually half of those are killed by some plucky teen who has the power to defy the odds and stand together with his friends.

it's destructive level is potentially metaverse level+ (which means it's a universe buster)
can warp reality
has dimensional and megaversal teleportation
can banish the target from the megaverse into a foreign dimension
can turn fantasy into reality
can easily survive the collapse of the entire multiverse utterly unharmed (not just jump to a new one, survive the collapse itself)
can grow bigger (10,000 times larger in one go, and can grow infinite times)
can fire homing lasers that reach Earth from Mars in a moment and home in on and destroy millions of targets
can operate in universes, multiverses with different laws of physics or where time-space flows differently
can create a hologram of beings, and do anything to them through the hologram
can control quantum, element, probability and chaos
can resist the destruction of space, time, and universes
can create matter
can create its own hyperspace, manifested and create various kind of weapons
time-space control. Freezing, turning back, and fast-forwarding, causality and energy control
even if you somehow manage to blow it up it just reverts to itself from before it was destroyed (with time control ability)
can survive from not existing.

Demonbane Athena Aetherum: Elder God Demonbane undoes the seal on Shining Trapezohedron, unleashing the power of Azathoth. This effectively works like a distress call, summoning infinite x infinite amount of Demonbanes from all the worlds and times that ever were, are, ever will be, never were, aren't, and never will be.
- Lemuria Impact Ain Soph Aur: Summon Infinite X Infinite number of Demonbanes to use Lemuria Impact simultaneously to destroy the enemy. (Each attack was noted to have the power of Big Bang.) (cool huh)

Elder God Demonbane and Alucard are my best choices. Both are stupid sauce OP, but theres one here im not sure has been mentioned yet. I haven't read every post on here but I think you all might be forgetting Kamui from X. Granted EGD and Alu are above him but hes still stupidly powerful.